DNA typing of urine samples following several years of storage

The possibility of typing DNA polymorphisms on urine samples was investigated in a controlled storage experiment and for samples that were 1-7 years old. Female urine samples showed a higher amount of epithelial cells and therefore a higher DNA yield. Employing the polymerase chain reaction, specific amplification results were achieved for all samples over a 6 month storage period. The microscopical examination of the samples revealed not only differing degrees of contamination with bacteria, yeasts and fungi, but also the presence of still intact epithelial cells. Only 20% of the male samples and 32% of the female samples yielded specific amplification results. By separating the human cells from the contaminating organisms prior to DNA extraction, the number of successfully typed samples could be improved to 35% of the male and 77% of the female samples. This result confirms that excess amounts of co-extracted non-human DNA can inhibit the specific amplification of human target sequences.